"Do you know why Turkey has not been able to enter the EU for 54 years? The reason is absolutely clear: the EU is a Christian union," Erdogan said at a rally in Ankara on Sunday.
The president said at the rally that the proposed constitutional changes [giving Turkey's president more power] would boost the country's economic development, which is something Ankara's opponents are against.
"The Turkish economy grew by 2.9 percent in 2016 while a number of Western countries can't overcome their economic crisis," he added.
Erdogan again accused Western countries of backing the Kurdistan Workers' Party (PKK), recognized as a terrorist organization by Ankara.
Turkey and the European Union signed an EU Association agreement back in 1963. Ankara submitted a membership proposal in 1987. Formal talks on Turkey's accession to the bloc started in 2005. In March 2016, its candidature received a boost as it signed a migration deal with the European Union.
On March 25, just on the day when the European Union celebrated its 60th birthday, Erdogan said Turkey could hold a referendum on whether it actually needs to further strive to join the bloc.
On March 17, he urged Turks living in Europe to have five children and reach prosperity, as they are "the future of Europe."